1. Field of the Invention
The present invention relates to an industrial robot using a parallel link mechanism.
2. Background Art
A known industrial robot using a parallel link mechanism (hereafter called “robot”) is disclosed in Japanese Translation of PCT Application No. 2002-532269. This robot includes a base unit, which is a support base, a plurality (three) of first arms which oscillate around the horizontal axis respectively by driving of a motor secured on the base unit, and second arms which respectively connect the first arms to one head unit (end effector). The position and attitude of the head change by the first arms that are driven in a collaborative manner.
In this kind of robot, each of the second arms is connected to the first arm and the head unit via a ball joint. To be more specific, the second arm is configured by a pair of rods, and cup type sockets are disposed at both ends of each rod so as to face each other. A pair of ball studs, which constitute a ball joint with the socket, is secured to the first arm and the like, so as to face away from each other. The second arm is connected to the first arm and the like by the socket of each rod fitting into the ball head portion of the ball stud from the outside.
In order to secure a wider movable area of the second arm, and in order to easily remove the head unit for cleaning and maintenance, the socket of each rod is formed to be relatively shallow, therefore each rod constituting the second arm has a connecting member disclosed in Japanese Translation of PCT Application No. 2002-529258 so as to maintain the connection between the second arm (rod) and the first arm and the like. This connecting member is configured so as to pull both rods closer by the elastic force of a spring. In other words, the connecting member pushes the socket toward the ball stud (ball head portion), so as to maintain the connection of the second arm (rod) and the first arm and the like. For maintenance, this connecting member makes it relatively easier to remove the second arm from the first arm, or to remove the head unit from the second arm by releasing each rod from the elastic force of the spring.
However in the case of the robot having the connecting member disclosed in Japanese Translation of PCT Application No. 2002-529258, if the second arm performs sudden movement due to rapid acceleration, for example, or if the second arm collides with an obstacle, the rods constituting the second arm may be unintentionally widely separated, and at worst the second arm may fall out from the first head, or the head unit may be disconnected from the second arm.
Furthermore, the connecting member disclosed in Japanese Translation of PCT Application No. 2002-529258 is attached to the rods by the hooks at both ends that are each hooked to the engaging portion of each rod. Therefore if the second arm performs sudden movement due to rapid acceleration, for example, the hook may disengage from the engaging portion, and such a problem as the second arm falling off from the first arm may occur, as described above.